Micro-electromechanical switches are used in a variety of applications and in particular for satellite communications systems with architecture that includes switching matrices and phased array antennas. It is desirable to have a switch having low-insertion loss, high isolation and high switching frequency.
Presently, the micro-electromechanical switches known in the prior art include a beam cantilevered from a switch base, or substrate. The beam acts as one plate of a parallel-plate capacitor. A voltage, known as an actuation voltage, is applied between the beam and an electrode on the switch base. In the switch-closing phase, or ON-state, the actuation voltage exerts an electrostatic force of attraction on the beam. As a result of the electrostatic force of attraction, the beam deflects and makes a connection with a contact on the switch base, closing the switch. Ideally, when the actuation voltage is removed, the beam will return to its natural state, breaking its connection with the contact electrode, thereby opening the switch.
The switch-opening phase, or OFF-state, is not directly controlled. It relies on the forces of nature embodied in the spring constant of the beam to effect the opening of the switch. Unfortunately, these forces are not always predictable and therefore unreliable.
For example, in some cases, once the actuation voltage is removed, stiction forces, (forces of attraction that cause the cantilevered beam to stick to the contact electrode), overcome the spring restoring force of the beam. The stiction force may cause the free end of the cantilevered beam to stick to the contact electrode and keep the switch closed when, in fact, it should be open.
Another problem associated with cantilever beam type switches is intrinsic to the beam's change of state from open to close. The operation of the beam is inherently unstable. When closing, the beam deforms gradually and predictably, up to a certain point, as a function of the actuation voltage being applied to the switch. Beyond that point, control is lost and the beam's operation becomes unstable, causing the beam to come crashing down onto the secondary electrode. This causes the beam to stick, or causes premature deterioration of the contact electrode. Both conditions impair the useful life of the switch and result in premature failure.
Prior art cantilever beam type switches require a trade-off between actuation voltage and isolation. For a low actuation voltage, the beam-to-substrate separation should be small. However, a small beam-to substrate separation results in a large parasitic capacitance, and thus a low isolation.
In addition, the maximum frequency at which the beam can deflect and relax is related to its geometry and material properties, such as length, bulk modulus, and density. Therefore, it may be impossible, in some applications, to achieve high switching frequencies at practical beam geometries.